It's that time of year again when the open-air festival season gets into full swing. Deciding which festival to attend is only part of the process; figuring out what to wear is vital! From the desert at Coachella to the often rain-soaked muddy fields of Glastonbury, weather is always a consideration. Light layers work best in most environments, and comfort really is key. Normal fashion rules don't apply to festival gear, but there are some guidelines to keep in mind. Eclectic styling like mismatched prints is not only permitted, it's practically required. Experiment with vintage by introducing select elements, but don't feel pressured to go head-to-toe with the effect. Mix in some modern pieces, even designer items. Here are some styles from past festivals to provide some inspiration.

Coachella (April 15-17, 2011)

One of the largest festivals in the United States, Coachella takes place out in the sweltering California desert. Now in its 12th year, this is a great star-gazing opportunity; tons of celebs attend the annual event. In addition to music on the five major stages, artists like Duran Duran and Kanye West are on this year's bill, there's also interactive artwork on display.

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Back in 2008, Brandy went vintage, paring a dress with shorts, and adding in some strappy Payless sandals. Another vintage frock was spotted that year combined with Jet Rag accessories courtesy of Cassandra.

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Kelly Osbourne worked the layers, pairing a grey cardigan, sheer floral tank, and bright blue shorts, with socks and sandals. The pale pink dress model Agyness Deyn had on was toughened up by a pair of combat boots.

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Solange Knowles stood out in all white and ruffles with extreme cat-eye shades. Kellan Lutz of Twilight fame topped off a Playboy tee with a straw fedora.

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Showing off the art of festival dressing, Whitney Port wore a coral colored dress for Day 2, before slipping into a cleverly mismatched loose top and shorts the following day.

NEXT: Bonnaroo

Bonnaroo (June 9-12, 2011)

Held on a farm in Manchester, Tennessee, the four day festival features rock, hip-hop, and bluegrass. This year showcases Neil Young, Scissor Sisters, Loretta Lynn, and Eminem for starters. Bonnaroo, which is Creole slang for "Good Stuff", has a lot of great extras, like a comedy tent and silent disco (headphones provided). The 2009 event was full of down-to-earth fashions.

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Drew Barrymore hit the scene, clad in an LnA shirt, gypsy skirt, and waders. Parenthood star Joy Bryant was another celeb who came out to enjoy the festival, looking low-key in Levi's shorts, Calvin Klein shades, and J. Crew wellies.

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A classic Chanel bag looked great with Paige Elkington's vintage top, boots, and self-made hot pants. Nasrin Leahy reworked her mom's 80s-era maxi summer dress into a mini and added a Primark fringed bag as well as Minnetonka moccasins.

NEXT: Glastonbury

Glastonbury (June 22-26, 2011)

Known for occasionally turning into a mudfest (that's why attendees are often spotted wearing wellies), Glastonbury takes place on Worthy Farm in Pilton, UK. The pop-heavy event has been put on for over 40 years with U2, Beyonce, and Coldplay being some of this year's headliners.

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Anna went flashy in 2008 with a vintage jacket, Zara shorts, and Uniqlo top. Accessories included Prada sunglasses and Vagabond boots. That same year, Hermione poses in her own vintage coat over a Peacocks top. Those fantastic heels are vintage, too.

Representing for the men, Robbie Yates arrived in a Marc Jacobs t-shirt and Dsquared jeans. The Louis Vuitton glasses make the outfit. Gemma Cairney played up conflicting patterns with a vintage lacy dress and Falke tights.

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Alexa Chung opted for a striped button-up and leopard bag last year, while Pixie Geldof went mini in a printed skirt, tank, and grey knee socks.

NEXT: Lollapalooza

Lollapalooza (August 5-7, 2011)

Turning 20 this year, the once alternative branded festival now also showcases hip-hop and hard rock. Set in Chicago's Grant Park since 2005, the epic party offers a PlayStation HQ, the Art Market, and various exhibits. Although the official line up will be released at the end of April, plan on a group of diverse performers since the 2010 list included Green Day, Lady Gaga, DEVO, Blues Traveler, and Erykah Badu.

Jamie Rosenthal went designer in a Christian Dior dress finished off with chunky black Charlotte Ronson boots. Gossip Girl cast member Jessica Szohr went all vintage from her funky hat to her grey boots.